21573997 has 8 divisors (see below), whose sum is σ = 22331232. Its totient is φ = 20826000.

The previous prime is 21573991. The next prime is 21574009. The reversal of 21573997 is 79937512.

21573997 = 9² + 10² + ... + 401².

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21573997 - 2¹⁹ = 21049709 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21573991) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2622 + ... + 7072.

It is an arithmetic number, because the mean of its divisors is an integer number (2791404).

Almost surely, 2^21573997 is an apocalyptic number.

It is an amenable number.

21573997 is a deficient number, since it is larger than the sum of its proper divisors (757235).

21573997 is a wasteful number, since it uses less digits than its factorization.

21573997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4619.

The product of its digits is 119070, while the sum is 43.

The square root of 21573997 is about 4644.7816956236. The cubic root of 21573997 is about 278.3835302950.

The spelling of 21573997 in words is "twenty-one million, five hundred seventy-three thousand, nine hundred ninety-seven".